Roughly speaking, a spacetime is said to be asymptotically simple if
it admits a conformal extension similar to that of the Minkowski
spacetime whereby a null hypersurface (null infinity)
\({I}\)  is attached to the spacetime. Generically, \({I}\) 
consists of two disjoints components \({I}^+\)  (future
null infinity) and \({I}^-\)  (past null infinity)
representing, respectively, the endpoints and startpoints of null
geodesics. As stressed by Geroch [1]}, the central aim of the
definition of asymptotically simple spacetimes (and, in fact, any
approach to define isolated systems) is to identify Universal
structures in a wide class of spacetimes which can, in turn, be used
to introduce notions of physical interest —say, conserved
quantities, radiation states. The definition tries to strike a balance
between ensuring the existence of enough structures to be able to
extract useful conclusions and not being too restrictive to avoid that
only a handful of exact solutions satisfy it.
